DE102015200462A1 - aftertreatment system - Google Patents

Abstract

An exhaust aftertreatment system for an internal combustion engine in a motor vehicle has an exhaust system with catalyst traversed by engine exhaust and is characterized in that automotive compressed air can be introduced into the exhaust system upstream of the catalyst to assist an exothermic chemical reaction on the catalyst. In addition, the invention relates to a motor vehicle, which is equipped with the exhaust gas aftertreatment system according to the invention, and to a corresponding method, for exhaust aftertreatment.

Description

The invention relates to an exhaust aftertreatment system for an internal combustion engine in a motor vehicle, and a motor vehicle with such an exhaust aftertreatment system and a method for post-treating exhaust gas of an internal combustion engine with a catalyst with a corresponding exhaust aftertreatment system.

State of the art

In today's commercial vehicle engines, natural gas is increasingly being used as fuel. Such engines usually operate on the principle of the gasoline engine. Natural gas has very good combustion characteristics, especially in stoichiometric combustion or in lean operation. But there are disadvantages in the exhaust aftertreatment with catalysts. In particular, the 50% conversion point of a natural gas combustion catalyst is at significantly higher temperatures than gasoline. In addition, the commercial vehicle gasoline engine has a significantly lower thermal capacity, since it is derived from a diesel engine, with the result that the exhaust gas outlet temperature is lower in these engines and thus less energy is available for heating the catalyst.

Disclosure of the invention

It is an object of the present invention to provide an improved exhaust aftertreatment system which can efficiently and reliably operate a catalyst even on fuels having a comparatively large activation energy for catalyst exhaust gas purification. In particular, situations are to be taken into account, in which the thermal energy available in the exhaust gas is insufficient to effect an efficient conversion of the pollutants contained in the exhaust gas in the catalyst.

The invention includes an exhaust aftertreatment system for an internal combustion engine in a motor vehicle having an exhaust system with catalyst traversed by engine exhaust, characterized in that automotive compressed air can be introduced into the exhaust system upstream of the catalyst to assist an exothermic chemical reaction on the catalyst.

The invention also includes a motor vehicle, in particular a commercial vehicle, with a motor vehicle compressed air system, in particular with a brake circuit compressed air system having an exhaust aftertreatment system according to the invention, wherein the motor vehicle compressed air system and a related with the exhaust system for supplying the automotive compressed air and selectively has shut-off line.

The invention also includes a method of post-treating exhaust gas of an internal combustion engine with catalyst having an exhaust aftertreatment system according to the invention comprising supplying automotive compressed air from an automotive compressed air system to the exhaust gas upstream of the catalyst to promote an exothermic chemical reaction on the catalyst.

The automotive compressed air is available during operation of the motor vehicle in virtually unlimited quantity and not limited in time. For example, commercial vehicles usually have a motor vehicle compressed air system for actuating the brake circuit, which constantly supplies compressed air at a pressure of about 10 bar. The use of automotive compressed air makes it possible to guide and distribute air into the exhaust system at all times. This applies first to an operating phase shortly after the start of an internal combustion engine, in which the catalyst is to be heated rapidly to its operating temperature. In addition, however, the catalyst can be kept warm during operation of the internal combustion engine by adding appropriate amounts of compressed air and even burned during operation of the internal combustion engine and thereby regenerated. Since the exhaust aftertreatment system according to the invention makes it possible to greatly increase the exhaust gas temperature in the catalytic converter, it is also possible to use catalysts which operate in conjunction with an internal combustion engine operated with an air-fuel ratio λ greater than or equal to 1 and even when using fuels such as natural gas Activation temperature for efficient chemical conversion of exhaust gas by means of catalyst lead to quickly and permanently achieve an efficient operating range for the catalyst, which is characterized by higher temperatures in the catalyst than in conventional gasoline gasoline engines usual. Even in situations in which the exhaust gases coming from the engine do not have the necessary thermal energy of their own accord in order to effect an efficient conversion in the catalyst, a sufficient increase in the temperature in the catalyst can be achieved by adding compressed air.

In one embodiment, the exhaust system may include a manifold, a turbocharger, a pre-catalyst lambda probe, a catalyst, and a post-catalyst lambda probe.

The described internal combustion engines include, in particular, gasoline engines which are operated with a gaseous fuel and / or at which the air-fuel ratio λ is stoichiometrically or even greater than 1 according to the operation.

In another embodiment, the allocation of the air in the exhaust system at any time can be done by means of a control unit, which may be designed as a separate or in a motor control / motor control unit integrated control unit. With the help of the control / regulating unit an efficient operation of the exhaust aftertreatment system is possible, since the exhaust-compressed air mixture can be influenced in the short term and can be adapted to changes in the air-fuel ratio in the internal combustion engine.

In one embodiment of the exhaust aftertreatment system according to the invention, it is possible to realize the structure with only a few components, since it can be used on numerous existing systems in the motor vehicle. As a result, the structure of an exhaust aftertreatment system according to the invention requires little additional components.

In one embodiment, the internal combustion engine may be operable with a gaseous fuel, in particular with natural gas. When using such an internal combustion engine, the activation temperature for a conversion of pollutants, in particular hydrocarbons, in the exhaust gas without a catalyst is generally higher than the temperature of the exhaust gases flowing in the exhaust system upstream of the catalytic converter. Because of the relatively high activation temperature without the presence of a catalyst, there is no reaction of the exhaust gases with air upstream of the catalytic converter so that compressed air can be added between the combustion chamber and the catalytic converter without a significant increase in the exhaust gas temperature. On the contrary, even with the addition of sufficiently large amounts of compressed air even a cooling of the exhaust gases occur. In the catalyst, however, this activation energy is significantly lowered so that an exothermic reaction can begin. This exothermic reaction can be greatly accelerated by adjusting an excess of air by means of compressed air. Thus, if sufficient air and fuel is available, the temperature in the catalyst can quickly rise above the 50% turnover threshold. The combustion of gaseous fuel, especially natural gas, is cleaner than that of fuels such as gasoline and diesel. That's why there are fewer fuel molecules available in the exhaust than in petrol or diesel. Therefore, it is important for the timely onset of the exothermic reaction in the catalyst to sufficiently high excess air, possibly supported by the addition of additional fuel, for example, by short-term operation of the engine in the rich area.

In one embodiment, the exhaust system communicates with a compressed air system of the motor vehicle, in particular a brake circuit compressed air system, in order to provide the motor vehicle compressed air. This allows a continuous supply of the exhaust system, since the compressed air system of the motor vehicle during operation can provide non-stop compressed air available.

If it were intended to realize such an addition of air to the exhaust gas by means of a separate pump system assigned to the exhaust aftertreatment system, relatively complex measures would be required to provide and integrate the required pumps. The corresponding systems would not be suitable for freeing the catalyst. The use of compressed air from a motor vehicle compressed air system creates completely different possibilities, since these systems are designed for permanent use.

In one embodiment, the motor vehicle may be a utility vehicle. Commercial vehicles usually have a compressed air system, in particular for the brake circuit, which therefore does not need to be additionally retrofitted. The exhaust aftertreatment system can be used just in those commercial vehicles in which internal combustion engines are operated with gaseous fuels. Especially in such cases would often be impossible without switchable heating system for the catalyst only an unfavorable exhaust aftertreatment, because the thermal reaction of the exhaust gases in the catalyst does not run efficiently.

In one embodiment, the exhaust aftertreatment system may be configured so that the automotive compressed air is introduced into the exhaust system immediately upstream of the catalyst. In particular, the arrangement may be such that no further element is arranged between the area in which the motor vehicle compressed air is supplied and the catalyst. In many motor vehicles with automotive compressed air systems (eg for the brake circuit), the compressed air generator is arranged so that a connection between the compressed air generator and a Zufuhrort the automotive compressed air in the exhaust system is very short, when the compressed air supplied in the vicinity of the catalyst in the exhaust system becomes. This saves material in the design of the connection. In order to check a composition of an exhaust gas-compressed air mixture, data of a Hinterkatlambda probe, equivalent to a rear-mounted catalytic converter lambda probe, or an Interkatlambda probe, equivalent to a lambda probe arranged in the catalyst can be used.

In a further embodiment, the exhaust aftertreatment system may be configured so that automotive compressed air can be introduced into the exhaust system completely or substantially to the upstream of a lambda probe arranged upstream of the catalytic converter. Then the lambda probe can be used to check the composition of the exhaust air-compressed air mixture before the catalyst, and if necessary to control accordingly / regulate. This allows a simpler and often more accurate regulation of the composition of the exhaust-compressed air mixture.

In a further embodiment, the exhaust aftertreatment system may be configured such that automotive compressed air can be introduced into the exhaust system upstream of a turbocharger arranged in the exhaust system. Thus, an additional cooling of the exhaust gas flowing through the turbocharger can be achieved if the catalyst does not yet use the exothermic reaction of the air-fuel mixture because of the high activation temperature. The addition of compressed air can then be used in addition to protecting the turbocharger from thermal stress caused by hot exhaust gases. The exhaust-compressed air mixture reacts only in the catalyst, where it releases heat through an exothermic reaction.

In another embodiment, the exhaust aftertreatment system may be configured to apply compressed air to assist in heating the catalyst after starting the engine, adjusting and maintaining a desired operating temperature of the catalyst during operation, and / or temporarily increasing the catalyst temperature during regeneration phases of the catalyst can be introduced into the exhaust system. Heating is necessary for the catalyst to reach operating temperature in a reasonable amount of time. By adjusting and maintaining the operating temperature in the catalytic converter, it is ensured that the catalytic converter is operated in an optimum operating temperature range, even if the exhaust gas temperature per se would be too low to keep the catalytic converter at operating temperature. Through the regeneration phases, the catalyst receives its cleaning effect of the exhaust gases flowing through it. This also contributes to the longer shelf life of the catalyst as compared to catalysts which do not receive regeneration phases.

The line between the exhaust system and the automotive compressed air system can be controlled or controlled by a valve. The valve may serve to shut off and open the conduit, but more preferably as a proportional or pulse width modulation valve operated by a control unit. This makes it possible to quantitatively control the addition of compressed air to the exhaust system, optionally in accordance with a control of the operating cycle of the internal combustion engine, to make the exhaust aftertreatment more effective.

figure description

1 shows a schematic view of a motor vehicle with inventive exhaust aftertreatment system.

2 shows a schematic view of the exhaust aftertreatment system according to the invention.

In the 1 is a motor vehicle 2 shown. The car 2 has an internal combustion engine 4 with an exhaust system 6 on. A motor vehicle compressed air system 8th is via a compressed air line 10 with the exhaust system 6 connected, as will be explained in more detail below.

In the 2 is the exhaust system 6 with a part of the internal combustion engine 4 shown schematically. The internal combustion engine operating in the example shown as a gasoline engine 4 includes a combustion chamber 12 in which there is a piston 14 emotional. On a wall of the combustion chamber 12 There are two probes attached. At the upper end of the combustion chamber 12 is at least one inlet valve 15 and at least one exhaust valve 16 arranged. In between there is a spark plug 18 whose electrode is in the combustion chamber 12 protrudes to a compressed air-fuel mixture 20 to ignite. The inlet valve 15 and the exhaust valve 16 be feathered 22 held in a closed position. Above the valves 15 and 16 is a front part of a feed channel 28 illustrated, in the direction of flow, a compressor part of a turbocharger 40 is arranged. Left of the combustion chamber 12 is the back part of the feed channel 28 represented by the air and an injection valve 30 supplied fuel mist in the combustion chamber 12 is directed. During combustion of the air-fuel mixture 20 formed exhaust gas passes through the piston 14 from the combustion chamber 12 through the outlet valve 16 in the exhaust system 6 , The exhaust system 6 includes an exhaust pipe with catalyst disposed therein 50 , For example, an oxidation catalyst. The exhaust system 6 points in the flow direction of the exhaust gas 32 from the combustion chamber 12 coming an exhaust gas recirculation 38 , a turbine part of the turbocharger 40 , a tributary path 42 that's over a flap 44 using a servomotor 46 is opened or closed, a first lambda probe 48 also called the control lambda probe, the catalyst 50 and a second lambda probe 52 , also referred to as diagnostic lambda probe on. In the exhaust system 6 becomes the exhaust 32 compressed air 34 . in particular automotive compressed air, admixed, creating an exhaust gas compressed air mixture 36 arises.

The first lambda probe 48 detects the composition of the exhaust air / compressed air mixture 36 and passes this information to a control unit, not shown, to the composition of the exhaust gas-compressed air mixture 36 to adjust on the catalytic converter. In the catalyst 50 becomes the exhaust gas-compressed air mixture 36 aftertreatment by oxidation and, if appropriate, reduction in order to filter pollutants from the exhaust gas and to reduce pollutant emission. The second lambda probe 52 detects the composition of the exhaust air / compressed air mixture 36 after the catalyst 50 and also passes this information to the control unit for the composition of the exhaust gas-compressed air mixture 36 to influence.

In the 2 is in a schematic and extremely simplified way continue to be a motor vehicle compressed air system 8th shown with the exhaust system 6 for the supply of compressed air 34 can be connected for the exhaust aftertreatment. The automotive compressed air system 8th is over the through a valve 54 Lockable compressed air line 10 with the exhaust system 6 connected. The automotive compressed air system 8th includes a compressed air generator and accumulator, not shown in detail, both in the motor vehicle 2 , in particular in a commercial vehicle, are present. In a commercial vehicle, for example, a brake circuit with the automotive compressed air system 8th fitted. The valve 54 is designed so that its flow rate of compressed air is suitably adjustable. Particularly suitable for this purpose are a proportional valve or a pulse width modulation valve. The compressed air line 10 is designed as a pipe or a hose which the air pressure from the automotive compressed air system 8th withstand.

The compressed air 34 from the automotive compressed air system 8th can be at three different points in the exhaust system 6 be initiated.

A first introduction area 56 is upstream of the catalyst 50 arranged. By introducing compressed air 34 in the exhaust 32 right in front of the catalyst 50 is in many cases a comparatively short line length to the exhaust system 6 possible because the automotive compressed air system 8th near the catalyst 50 is arranged. However, then there is the first lambda sensor 48 farther upstream, not for detecting the composition of the exhaust air-compressed air mixture 36 to disposal. In such cases, however, in catalysts 50 which have an intercatalde probe which can be used, since this is the composition of the exhaust air / compressed air mixture 36 before the second lambda probe 52 detects and controls. This allows the precise adjustment of the operating temperature in the catalyst 50 ,

A second introductory area 58 is upstream of the first lambda probe 48 arranged. By introducing compressed air 34 in the exhaust 32 upstream of the first lambda probe 48 can be the first lambda probe 48 for the direct detection of the composition of the exhaust gas compressed air mixture flowing into the catalyst 36 be used, so that in an unfavorable composition a follow-up or readjustment can be initiated by the control unit. This results in a longer shelf life of the catalyst 50 because of this unfavorable exhaust gas compressed air mixtures 36 is protected.

A third opening area 60 is upstream of the turbine part of the turbocharger 40 arranged. When mixing the exhaust gas 32 with the compressed air 34 cools the exhaust gas-compressed air mixture 36 something off, causing the exhaust system 6 arranged turbine part of the turbocharger 40 is protected against higher thermal loads. Only in the catalyst 50 responds the exhaust-compressed air mixture 36 in an exothermic reaction, so that the exhaust gas temperature rises there. In front of the catalyst 50 the activation temperature is not reached, which is needed to a reaction of the exhaust air-compressed air mixture 36 to activate.

The compressed air 34 can depending on the application from the automotive compressed air system 8th at one of the three introduction areas 56 . 58 and 60 be supplied. It is also possible that compressed air 34 is supplied at two of the three introduction areas or at all of the three introduction areas.

The exhaust aftertreatment system 1 can be used when the catalyst 50 shortly after the start of the internal combustion engine 4 must be heated to reach its operating temperature. In addition, the exhaust aftertreatment system 1 also designed to be the catalyst 50 in continuous operation of the internal combustion engine 4 to keep at a desired temperature. Especially when the temperature of the engine from the exhaust system 6 exhaust gas reaching below the temperature at which the 50% conversion point of the chemical reactions taking place in the catalyst is achieved, can thus be achieved during the entire operation of the internal combustion engine 4 continuous heating - either continuously or at certain intervals - yet ensuring efficient catalyst operation. The exhaust aftertreatment system 1 is also suitable for the catalyst 50 to heat at intermittent intervals so far that a regeneration or burnout of the catalyst 50 can be done.

The internal combustion engine 4 in today's motor vehicles, especially commercial vehicles, is increasingly operated with gaseous fuels. Such internal combustion engines usually operate with a stoichiometric to lean air-fuel mixture 20 ie the air-fuel ratio λ is greater than or equal to 1 , This results in lower combustion temperatures, which are insufficient to the catalyst 50 to heat in a given time or to keep at a desired operating temperature during operation. It may be useful in such internal combustion engines, the internal combustion engine 4 For example, in that an engine control unit in operation, the injection valve 30 During short-term recurring operating phases suitably controls - for short phases with a rich air-fuel mixture 20 (λ less than 1) to operate. When burning so exhaust gas 34 , which contains residues of the fuel, since no stoichiometric combustion is possible. This exhaust 32 can then be a suitable amount of compressed air 36 coming from the fuel compressed air system 8th is added, so that the exothermic reaction in the catalyst 50 begins and quickly increases the desired temperature of the catalyst 50 leads.

Claims (10)

Exhaust aftertreatment system ( 1 ) for an internal combustion engine ( 4 ) in a motor vehicle ( 2 ) comprising an exhaust system through which engine exhaust gas flows ( 6 ) with catalyst ( 50 ); characterized in that upstream of the catalyst ( 50 ) Automotive compressed air ( 34 ) in support of an exothermic chemical reaction on the catalyst ( 50 ) into the exhaust system ( 6 ) can be introduced. Exhaust aftertreatment system ( 1 ) according to claim 1, wherein the internal combustion engine ( 4 ) is designed for operation with a gaseous fuel, in particular with natural gas. Exhaust aftertreatment system ( 1 ) according to claim 1 or 2, wherein the exhaust system ( 6 ) with a compressed air system of the motor vehicle ( 8th ), in particular a brake circuit compressed air system, is connectable to the motor vehicle compressed air ( 34 ). Exhaust aftertreatment system ( 1 ) according to one of the preceding claims, wherein the motor vehicle ( 2 ) is a commercial vehicle. Exhaust aftertreatment system ( 1 ) according to one of the preceding claims, which is designed such that motor vehicle compressed air ( 34 ) immediately upstream of the catalyst ( 50 ) into the exhaust system ( 6 ) can be introduced. Exhaust aftertreatment system ( 1 ) according to one of the preceding claims, which is designed such that motor vehicle compressed air ( 34 ) upstream of an upstream of the catalyst ( 50 ) arranged lambda probe ( 48 ) into the exhaust system ( 6 ) can be introduced. Exhaust aftertreatment system ( 1 ) according to one of the preceding claims, which is designed such that motor vehicle compressed air ( 34 ) upstream of one in the exhaust system ( 6 ) arranged turbocharger ( 40 ) into the exhaust system ( 6 ) can be introduced. Exhaust aftertreatment system ( 1 ) according to one of the preceding claims, which is designed such that the motor vehicle compressed air ( 34 ) in support of the heating of the catalyst ( 50 ) after a start of the internal combustion engine ( 4 ) for adjusting and maintaining a desired operating temperature of the catalyst ( 50 ) and / or for temporarily increasing the catalyst temperature during regeneration phases of the catalyst ( 50 ) into the exhaust system ( 6 ) can be introduced. Motor vehicle ( 2 ), in particular commercial vehicle, with a motor vehicle compressed air system ( 8th ), in particular with a brake circuit compressed air system, comprising an exhaust aftertreatment system ( 1 ) according to one of the preceding claims; wherein the motor vehicle compressed air system ( 8th ) one with the exhaust system ( 2 ) for supplying automotive compressed air ( 34 ) connected and selectively lockable line ( 10 ) having. Process for the aftertreatment of exhaust gas ( 32 ) an internal combustion engine ( 4 ) with an exhaust aftertreatment system ( 1 ) with catalyst ( 50 ) according to any one of claims 1 to 8, comprising: supplying automotive compressed air ( 34 ) from a motor vehicle compressed air system ( 8th ) into the exhaust gas ( 32 ) upstream of the catalyst ( 50 ) to an exothermic chemical reaction on the catalyst ( 50 ) to support.

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